An assembly and associated method for a commissure of a prosthetic heart valve is disclosed. As one example, a method includes forming each of a plurality of commissures with a plurality of leaflets by pairing a first commissure tab of a first leaflet with an adjacent, second commissure tab of a second leaflet, folding a support strip over an inner reinforcing element, positioning the folded support strip between the first and second commissure tabs, and attaching first and second outer reinforcing elements to the first and second commissure tabs, respectively, via stitching, the stitching extending over at least a portion of the first reinforcing element opposite a fold region of the support strip, and, for each commissure, securing end portions of the support strip to a respective support portion of a frame of the prosthetic heart valve.